The present invention relates to a mechanical dynamometer tool, in particular a torque wrench, for manually applying torque, more specifically the dynamometer tool includes a mechanical means suitable for delivering predetermined torsion torque to a drive portion designed to co-operate with a tightening drive member for driving a fastener element, the mechanical means being in mechanical equilibrium under the action of suitable bias means, the mechanical means being releasable by breaking the mechanical equilibrium, and means for detecting a break in mechanical equilibrium.
It is known that operations for tightening fastener elements in industrial environments require increasing levels of traceability, i.e. knowledge of all of the information and of the measures that make it possible to monitor and to reconstruct rapidly the steps of the process.
For tightening operations, dynamometer tool manufacturers propose mechanical tools whose principle is based on equilibrium breaking in a manner that is very perceptible, making it possible for the break in equilibrium to be detected by a device having an electrical circuit provided with switch means whose state is changed by the break in equilibrium, and with a processing unit adapted to use the information relating to the state of said switch means. The entire detection device is generally housed in a housing fastened to the outside of the body of the tool.
Such a construction is not entirely satisfactory because the housing defines a protuberance on the periphery of the body of the tool, which protuberance is potentially a hindrance to inserting the tool into a mechanical member on which the operator is acting.
In addition, such a construction uses a miniature switch whose life is relatively short and that poses problems of reliability when it is subjected to sudden actuation, which generally applies for tools operating by breaking mechanical equilibrium.
Known devices also suffer from the drawback of not taking account of the phenomenon of over-torque that is exerted during the operation of tightening to torque once the equilibrium is broken. The value of such over-torque can be as high as 50% of the predetermined set torque when the wrench is used under certain conditions.
In addition, the use of electronic dynamometer wrenches is not desired on assembly lines because, with such wrenches, no physical sensation of going beyond the tightening torque can be felt.